JP2002228501A - Thermal air flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a thermal air flow meter with a simple structure capable of accurately measuring the rate of flow in two directions by providing a temperature compensation means at a portion for acquiring a temperature difference signal. SOLUTION: A node between temperature sensing resistors Ru1 and Rd1 is connected through a temperature sensing resistor Ra to a minus input terminal of an amplifier A while the node between the sensing resistors Ru1 and Rd1 is connected to a plus input terminal of the amplifier A. A node between temperature sensing resistors Rd2 and Ru2 is connected to a node between the sensing resistor Ra and the minus input terminal of the amplifier A. A temperature sensing resistor Rf is disposed at a position bound up with the temperature of air flow and not suffering thermal interference of a heating resistor Rh, and forms a bridge circuit together with resistors R1 to R3 and the heating resistor Rh. By connecting the sensing resistor Ra and setting the temperature coefficients of the resistors Ru and Rd at about a third part of that of the resistor Ra, a compensation can be made so that the air-flow temperature dependency of potential difference dV at a comparison point is decreased to one tenth or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring an intake air flow rate of an engine required for controlling an internal combustion engine of an automobile, and more particularly, to an apparatus for accurately measuring a backflow phenomenon caused by intake pulsation. Field of the Invention The present invention relates to a thermal air flowmeter capable of detecting a flow rate in one direction.

[0002]

2. Description of the Related Art Conventional air flow measuring devices include:
For example, there is one disclosed in Japanese Patent Application Laid-Open No. 9-318412. The technology disclosed in this publication is controlled at a temperature difference between the intake air temperature and a certain temperature, and installs a temperature-sensitive resistor upstream and downstream of a heating resistor installed in an air flow, and installs the temperature-sensitive resistor upstream and downstream of this resistor. This is a method of measuring the bidirectional air flow rate based on the temperature difference between the temperature-sensitive resistors.

According to the disclosed technology, a slit is provided between the heating resistor and the downstream temperature sensing resistor, or a heating current of the heating resistor and a temperature difference signal of the temperature sensing resistor are combined. Thus, the flow measurement range can be expanded and the flow measurement sensitivity can be optimized.

[0004]

However, in the above-mentioned prior art, when the temperature difference of the temperature-sensitive resistor is used as a flow rate measurement signal, a measurement error due to the ambient temperature occurs. A complicated large-scale temperature correction means independent of the flow rate measurement unit, such as a means for changing the reference voltage to be performed according to the ambient temperature, is required.

Further, when a heating current of the heating resistor and a temperature difference signal of the temperature sensing resistor are combined (a bridge circuit is constituted by the heating resistor and the temperature sensing resistor, a heating bridge signal from the heating resistor is generated). And the temperature difference bridge signal by the temperature sensitive resistor), the temperature compensation effect for the ambient temperature can be expected, but the response of the heating current is much faster than the temperature difference bridge signal, and the heat generation bridge signal is a noise component. Since the signal is superimposed on the temperature difference bridge, the noise component of the flow rate measurement signal is increased, and the flow rate measurement accuracy is reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal air flow meter capable of performing accurate two-way flow measurement with a simple structure by providing a temperature compensating means at a portion where a temperature difference signal is obtained. It is.

[0007]

In order to achieve the above object, the present invention is configured as follows. (1) In a thermal air flow meter, a heating resistor controlled at a constant temperature difference from the air flow temperature, and a heat generating resistor installed in a heat interference region on the upstream side and the downstream side of the air flow of the heating resistor to form a bridge circuit. One or more pairs of first temperature-sensitive resistors to be formed, and a second temperature-sensitive resistor connected to two points to be compared with the potential between the temperature-sensitive resistors of the bridge circuit and dependent on the airflow temperature. And the air flow rate is measured based on the potential difference between the two points to be compared.

(2) Preferably, in the above (1),
The second temperature-sensitive resistor has a larger temperature coefficient of resistance than the first temperature-sensitive resistor constituting the side of the bridge circuit.

(3) In the thermal air flow meter, a heating resistor controlled at a constant temperature difference from the airflow temperature is installed in a heat interference region on the upstream and downstream sides of the heating resistor in the airflow. One or more first temperature-sensitive resistors forming a bridge circuit, and a second temperature-sensitive resistor connected to a voltage supply point or a reference potential point of the bridge circuit and having a negative temperature coefficient of resistance depending on airflow temperature. By comparing two points to be compared with the potential between the temperature-sensitive resistors of the bridge circuit,
Measure the air flow.

(4) In the thermal air flow meter, a heating resistor controlled at a constant temperature difference from the airflow temperature is installed in a heat interference region on the upstream and downstream sides of the heating resistor in the airflow. One or more pairs of temperature-sensitive resistors forming a bridge circuit;
A semiconductor element connected to a voltage supply point or a reference potential point of the bridge circuit and having a negative temperature coefficient of resistance depending on an air flow temperature; The air flow is measured by comparing the points.

(5) Preferably, (1), (2),
In (3) and (4), the heating resistor and the temperature-sensitive resistor are formed on the same substrate.

A temperature-sensitive resistor is arranged upstream and downstream of a heating resistor controlled to a certain temperature difference from the air temperature, and a temperature difference signal is obtained by a bridge circuit having each of the temperature-sensitive resistors as one side. Connect the comparison potential point of the bridge circuit with a resistor that depends on the intake air temperature so that the comparison potential difference of the bridge circuit increases with the rise of the intake air temperature, or depend on the intake air temperature at the voltage supply point or the reference potential point of the bridge circuit. By inserting an element having a negative temperature coefficient, temperature compensation of the temperature difference signal becomes possible.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a first embodiment of the present invention.
FIG. 3 is a circuit diagram of a thermal air flow meter according to the embodiment.

In FIG. 1, one end of a temperature-sensitive resistor Rf is grounded via resistors R3 and R2. Also,
The other end of the temperature-sensitive resistor Rf is connected to a heating resistor Rh and a resistor R.
1 is grounded. The connection point between the resistors R2 and R3 is connected to the inverting input terminal of the operational amplifier OP, and the connection point between the heating resistor Rh and the resistor R1 is connected to the non-inverting input terminal of the operational amplifier OP. The output terminal of the operational amplifier OP is connected to a connection point between the temperature-sensitive resistor Rf and the heating resistor Rh.

One end of the resistor R4 is connected to a temperature-sensitive resistor R
u1, Rd1, and a resistor R5. The other end of the resistor R4 is connected to a resistor R6 and a temperature-sensitive resistor Rd.
2, Ru2, and a resistor R7. Also,
A reference voltage Vref is applied to a connection point between the resistors R4 and R4 from a reference voltage source.

The connection point between the temperature-sensitive resistors Ru1 and Rd1 is:
It is connected to the minus input terminal of the amplifier A via the temperature sensitive resistor Ra. The connection point between the temperature-sensitive resistors Ru1 and Rd1 is connected to the positive input terminal of the amplifier A. Also,
The connection point between the temperature sensitive resistors Rd2 and Ru2 is the temperature sensitive resistor Rd.
a and the negative input terminal of the amplifier A.

The temperature-sensitive resistor Rf is disposed at a position that depends on the airflow temperature and does not receive thermal interference from the heating resistor Rh.
A bridge circuit is formed with the resistors R1 to R3 and the heating resistor Rh.

Further, feedback is made by the operational amplifier OP so as to maintain the balance of the bridge circuit, so that the heating resistor Rh is obtained.
Is controlled to maintain a constant temperature difference from the air temperature.

The above items are common to other embodiments described later as the heater control unit, and the functions and configurations are the same.

The temperature-sensitive resistors Ru1 and Ru2 are disposed in a heat interference region on the upstream side of the heat-generating resistor Rh.
Rd2 is arranged in a heat interference region on the downstream side of the heating resistor Rh.

Temperature-sensitive resistors Ru1, Ru2, Rd1, Rd
2 forms a bridge circuit with the fixed resistors R4 to R7, respectively. The opposite sides of this bridge circuit are each constituted by a temperature-sensitive resistor arranged upstream and downstream, and the configuration is inverted upside down between the opposite sides of the bridge circuit.

According to the circuit configuration shown in FIG. 1, when the airflow flows from the forward direction, the temperature-sensitive resistors Ru1 and Ru2 arranged on the upstream side of the heating resistor Rh correspond to the airflow. The resistance value is lowered due to cooling, and the heating resistor R
The temperature-sensitive resistors Rd1 and Rd2 arranged downstream of h
Since the heat flow and the air flow of the heating resistor Rh are combined, the temperature change is small, and the resistance value is not increased or decreased.

As a result, the potential difference at the comparison point of the bridge circuit increases or decreases in accordance with the air flow rate. If the airflow flows from the opposite direction, the opposite phenomenon occurs, so that the magnitude relation of the potential difference at the comparison point of the bridge circuit is reversed.

Therefore, a bidirectional air flow rate can be measured from the potential difference at the comparison point of the bridge circuit. The amplifier A is an adjustment unit that converts the comparison point potential difference into a predetermined output characteristic.

In the first embodiment of the present invention, the comparison potential points of the bridge circuit are further connected by a temperature-sensitive resistor Ra arranged so as to depend on the airflow temperature. Temperature sensitive resistor R
a, Ru1, Ru2, Rd1, and Rd2 have substantially the same resistance value and resistance temperature coefficient. Are connected in series, the temperature coefficient of each side of the bridge circuit is apparently
Smaller than.

At this time, the potential difference d at the comparison point of the bridge circuit
v is given by the following equation (1). dV = Vref · (Rd / Ru-1)
/ (2 · Rd / Ra + Rd / Ru + 1) --- (1) where R
d1 + R5 = Rd2 + R6 = Rd, Ru1 + R4 = Ru
Let 2 + R7 = Ru.

By maintaining the heating resistor Rh as a heater at a certain temperature difference from the airflow temperature, the airflow temperature dependency in the heat transfer characteristic of the heat interference region of the heating resistor Rh is compensated. Since the thermal resistors Ru1, Ru2, Rd1, and Rd2 also depend on the airflow temperature, the reference resistance value of the thermal resistor, that is, the resistance value when no temperature difference occurs, depends on the airflow temperature.

As shown by the above equation (1), the temperature-sensitive resistor R
If a is infinite or not connected, Ru and R
d increases as the airflow temperature increases, and Rd / Ru changes due to the change in the airflow, and the comparison point potential difference dV has a decreasing airflow temperature dependency.

That is, when the temperature-sensitive resistor Ra is infinite,
The above equation (1) becomes the following equation (2). dV = Vref. (A-1) / (A + 1) --- (2) where A = Rd / Ru, specifically, A = (Rd (Q
0) + dRd) / (Ru (Q0) + dRu) = (R (Q
0) + dRd) / (R (Q0) + dRu).

Note that Rd (Q0) = Ru (Q0) = R
(Q0) = resistance value when the flow rate Q is 0, and dRd and dRu are resistance changes due to a temperature change generated according to the flow rate Q.

Here, the resistance value R (Q0) is greatly affected by the ambient temperature, and increases as the ambient temperature increases. On the other hand, the resistance changes dRd and dRu are not significantly affected by the ambient temperature.

Therefore, in the above formula, for example, at room temperature 2
The value A (20) at 0 ° C. and the value A at 80 ° C.
A (20)> A (8)
0), and the comparison point potential difference dv is also 80
It is smaller in the case of ° C.

Considering an extreme case, when R (Q0) = ∞, A → 1 is converged, so that the comparison point potential difference dv = 0 from the above equation.

As described above, when the temperature-sensitive resistor Ra is not connected, the comparison point potential difference dV is
Its magnitude has a decreasing airflow temperature dependence.

On the other hand, a temperature sensitive resistor Ra is connected,
By setting the resistances Ru and Rd so that the temperature coefficients of the temperature-sensitive resistors Ru and Rd are about 1/3 of Ra, it is possible to compensate the air flow temperature dependence of the comparison point potential difference dV to 1/10 or less. it can.

That is, when the temperature-sensitive resistor Ra is connected,
The above equation (2) becomes the following equation (3). dV = Vref. (A-1) / (2.B + A + 1) (3) where B = Rd / Ra. In this case, the resistor Ra
Is about three times the temperature coefficient of the resistor Rd, the above B decreases as the temperature rises. For this reason, B acts on the comparison point potential dv in a direction to increase as the temperature rises, and acts to offset the temperature dependence in the absence of the resistor Ra.

According to the experiments performed by the inventors of the present application, the reference voltage V
Assuming that ref is 5 V, other resistors are set to appropriate values, and the comparison point potential dv is calculated at a temperature of 20 ° C. and at a temperature of 80 ° C. As a result, both are 131.8 mV. It was almost 0.

Therefore, by connecting the temperature-sensitive resistor Ra and setting the resistors Ru and Rd such that the temperature coefficient of the temperature-sensitive resistors Ru and Rd is about 1/3 of Ra, the air having the potential difference dV at the comparison point can be obtained. The flow temperature dependency can be compensated to 1/10 or less.

By adding a simple circuit element such as adding a temperature-sensitive resistor Ra, an effect equivalent to changing the reference voltage Vref depending on the airflow temperature can be obtained.

That is, according to the first embodiment of the present invention, by providing the temperature compensating means at the portion where the temperature difference signal is obtained, it is possible to perform accurate bidirectional flow measurement with a simple configuration. A type air flow meter can be realized.

Further, since the heating resistor Rh and all the temperature sensing resistors (Ra, Rf, Ru1, Ru2, Rd1, Rd2) can be formed by the same process, for example,
It can be formed on the same semiconductor substrate, the manufacturing process can be simplified, and the circuit scale can be reduced.

FIG. 2 is a circuit diagram of a thermal air flow meter according to a second embodiment of the present invention. The difference between the example of FIG. 2 and the example of FIG. 1 is that, in the example of FIG. 2, the resistors R4, R5, R6, R7, and R8 of the example of FIG.
In that a resistor Rb is connected instead of the resistor Rb.

The temperature-sensitive resistor Rb is arranged so as to be dependent on the temperature of the airflow, and is connected to the comparison potential point of the bridge circuit. By using a temperature coefficient of the temperature sensitive resistor Rb which is about three times higher than that of the other temperature sensitive resistors, the temperature is compensated in the same manner as in the above embodiment.

For example, as the temperature-sensitive resistor Rb, a temperature sensor made of platinum is installed in an air stream, and the other temperature-sensitive resistor uses a polysilicon resistor formed on a semiconductor substrate.
Alternatively, the temperature sensitive resistor Rb is also formed on the same substrate, but it is conceivable to change the temperature coefficient by changing the impurity diffusion concentration.

In particular, when they are formed on the same substrate, the ratio between the temperature-sensitive resistor Rb and other temperature-sensitive resistors can be easily managed, and mass productivity is good.

Further, by inserting a fixed resistor in series with the temperature-sensitive resistor Rb, the apparent temperature coefficient of the temperature-sensitive resistor Rb can be manipulated, and the degree of temperature compensation can be easily adjusted.

In the above-described second embodiment of the present invention, the same effects as in the first embodiment can be obtained.

FIG. 3 is a circuit diagram of a thermal air flow meter according to a third embodiment of the present invention. The difference between the example of FIG. 3 and the example of FIG. 2 is that, in the example of FIG. 3, the connection point between the temperature-sensitive resistors Ru1 and Rd2 is the voltage of the reference voltage Vref via the temperature-sensitive resistor Rc. And the temperature sensitive resistors Ru1 and R1
The connection point of d1 is connected only to the plus input terminal of the amplifier A, and the connection point between the temperature sensitive resistors Rd2 and Ru2 is a point connected only to the minus input terminal of the amplifier A.

The temperature-sensitive resistor Rc is arranged so as to be dependent on the temperature of the airflow, and is connected to the voltage supply point of the bridge circuit. The temperature sensitive resistor Rc is made of a semiconductor material or the like so as to have a negative temperature coefficient.

According to the third embodiment of the present invention, the voltage supplied to the bridge circuit increases because the voltage drop across the temperature sensitive resistor Rc decreases as the airflow temperature increases.
As a result, it acts to compensate for the decrease in the comparison potential difference of the bridge circuit.

In the third embodiment, the same effects as in the first embodiment can be obtained.

The effect of the third embodiment can be similarly obtained by replacing the temperature-sensitive resistor Rc with a diode D as shown in FIG. In particular, in the example of FIG. 4, the value of the temperature coefficient can be easily set by connecting several diodes D in series or inserting fixed resistors in series.

FIG. 5 is a configuration diagram when the heating resistor and the temperature-sensitive resistor in the first embodiment shown in FIG. 1 are formed on the same semiconductor substrate B.

As described above, the temperature-sensitive resistors Ru1, Ru2, Rd1, and Rd2 are arranged near and upstream of the heating resistor Rh. In particular, the portion C is a thinned portion of the semiconductor substrate B, which suppresses heat conduction from the heating resistor Rh and forms a heat interference region due to heat transfer.

The temperature-sensitive resistors Rf and Ra are arranged at a thick portion of the semiconductor substrate B at a position sufficiently distant from the heat-generating resistor Rh and avoiding the downstream so as not to be affected by the heat flow.

Thus, the temperature sensing resistors Rf and Ra can detect the temperature of the air flow.

The features of the present invention are simple and simple in circuit in any of the embodiments. In addition, there is no need to operate the reference voltage source Vref directly by directly acting on the main temperature difference bridge portion of the air flow rate measurement.
Temperature compensation can be performed even in a situation where the air temperature to be measured cannot be monitored at ef.

Further, since the ratiometric property of the flow signal (potential difference at the comparison point) dV by the reference voltage source Vref is maintained, the signal of the thermal air flow meter according to the present invention is read by the A / D converter. , The interface error can be reduced.

[0059]

According to the present invention, by providing a temperature compensating means at a portion for obtaining a temperature difference signal, a thermal air flow meter capable of performing accurate bidirectional flow measurement with a simple configuration is realized. can do.

Further, since the temperature can be easily compensated for in a two-way air flow measurement under a pulsating flow that is sucked into an automobile engine and involves a backflow, the overall circuit configuration of the air flow meter is simplified and simplified. As a result, cost and error factors can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a thermal air flow meter according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a thermal air flow meter according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a thermal air flow meter according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a modification of the third embodiment of the present invention.

FIG. 5 is a configuration diagram when a heating resistor and a temperature-sensitive resistor according to the first embodiment are formed on the same semiconductor substrate B;

[Explanation of symbols]

 A Amplifier B Semiconductor substrate C Thin portion OP Operational amplifier R1, R2, R3 Resistor R4, R5 Resistor R6, R7 Resistor Ra, Rb, Rc Thermosensitive resistor Rd1, Rd2 Thermosensitive resistor Rf, Rh Thermosensitive resistor Body Ru1, Ru2 Temperature-sensitive resistor

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[Procedure amendment]

[Submission date] April 20, 2001 (2001.4.2
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

One end of the resistor R4 is connected to a temperature-sensitive resistor R
u1, Rd1, and a resistor R5. The other end of the resistor R4 is connected to a resistor R6 and a temperature-sensitive resistor Rd.
2, Ru2, and a resistor R7. Also,
The connection point between the resistor R4 and the resistor R 6, the reference voltage Vref is applied from the reference voltage source.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0048

[Correction method] Change

[Correction contents]

FIG. 3 is a circuit diagram of a thermal air flow meter according to a third embodiment of the present invention. Differs from the example of embodiment and 2 in FIG. 3, in the example of FIG. 3, the reference voltage connection point through a temperature-sensitive resistor R c of the temperature sensitive resistors Ru1 and Rd2 V
ref is connected to the voltage source, and the connection point between the temperature-sensitive resistors Ru1 and Rd1 is connected only to the positive input terminal of the amplifier A.
The connection point between the temperature sensitive resistors Rd2 and Ru2 is a point connected only to the minus input terminal of the amplifier A.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Explanation of sign

[Correction method] Change

[Correction contents]

[Explanation of Symbols] A Amplifier B Semiconductor substrate C Thin portion OP Operational amplifier R1, R2, R3 Resistor R4, R5 Resistor R6, R7 Resistor Ra, Rb, Rc Temperature-sensitive resistor Rd1, Rd2 Temperature-sensitive resistor R f Temperature-sensitive resistor Ru1, Ru2 Temperature-sensitive resistor Rh Heating resistor

Continuing from the front page (72) Inventor Keiichi Nakata 2520 No. Odaiba, Hitachinaka-shi, Ibaraki F-term in the Automotive Equipment Group of Hitachi, Ltd. (Reference) 2F035 AA02 EA05 EA08

Claims (5)

[Claims] 1. A heating resistor controlled at a constant temperature difference from an airflow temperature, and at least one pair of heating resistors installed in a heat interference region on an upstream side and a downstream side of an airflow of the heating resistor to form a bridge circuit. The potential between the first temperature sensitive resistor of the above and the temperature sensitive resistor of the bridge circuit should be compared.
And a second temperature-sensitive resistor connected to the point and dependent on the airflow temperature, wherein the airflow rate is measured by the potential difference between the two points to be compared. 2. The thermal air flow meter according to claim 1, wherein
The thermal air flow meter according to claim 1, wherein the second temperature-sensitive resistor has a higher temperature coefficient of resistance than the first temperature-sensitive resistor constituting the side of the bridge circuit. 3. A heating resistor controlled at a constant temperature difference from an airflow temperature, and at least one set of heating resistors installed in a heat interference region on the upstream and downstream sides of the airflow of the heating resistor to form a bridge circuit. And a second temperature-sensitive resistor connected to a voltage supply point or a reference potential point of the bridge circuit, and having a negative temperature coefficient of resistance depending on the airflow temperature, A thermal air flow meter, wherein an air flow rate is measured by comparing two points at which potentials between temperature-sensitive resistors of the bridge circuit are to be compared. 4. A heating resistor controlled at a constant temperature difference from an airflow temperature, and at least one set of heating resistors installed in a heat interference region on the upstream and downstream sides of the airflow of the heating resistor to form a bridge circuit. And a semiconductor element connected to a voltage supply point or a reference potential point of the bridge circuit and having a negative temperature coefficient of resistance depending on an airflow temperature, wherein the temperature-sensitive resistor of the bridge circuit is provided. A thermal air flow meter, wherein an air flow rate is measured by comparing two points to be compared with each other. 5. The thermal air flow meter according to claim 1, wherein the heating resistor and the temperature-sensitive resistor are formed on the same substrate. And thermal air flow meter.